en.Wedoany.com Reported - The team led by Manfred Scheer at the University of Regensburg (Universität Regensburg) successfully synthesized and characterized a series of previously unknown monomeric "silyltrielanes" with terminal SiH₃ groups by using the silyl salt Na(Me₄TACD)SiH₃ as a [SiH₃]⁻ transfer reagent in salt metathesis reactions with Lewis base-stabilized Group 13 halides (B, Al, Ga, In).
TACD stands for 1,4,7,10-tetraazacyclododecane. The compounds isolated and fully characterized by the research team include: the highly unstable Me₃N·BH₂SiH₃ (detected only in mixtures), the NHC-stabilized (NHC = N-heterocyclic carbene) IDipp·BH₂SiH₃ and IMe₄·BH₂SiH₃ silylboranes, the air-sensitive IDipp·AlEt₂SiH₃ silylalane, and the NHC-stabilized IDipp·GaH₂SiH₃ silylgallane. Here, IDipp represents 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene.
By performing triple salt metathesis reactions using IDipp·ECl₃ (E = Ga, In), the team also prepared IDipp·Ga(SiH₃)₃ and IDipp·In(SiH₃)₃, i.e., trisilyltrielanes with three SiH₃ groups attached to gallium or indium atoms. The thermodynamic and bonding properties of these compounds were investigated using DFT calculations, multinuclear NMR, IR spectroscopy, and single-crystal X-ray diffraction.
Experiments demonstrated that Na(Me₄TACD)SiH₃ is a practical solution-phase source of SiH₃⁻, suitable for clean salt metathesis reactions to generate monomeric compounds with terminal SiH₃ groups directly bonded to B, Al, Ga, and In. The study shows that the Si–E bonds (E = B, Al, Ga, In) are highly polarized; for boron, this bond can be described in a manner analogous to the Dewar–Chatt–Duncanson model, where the σ-donating effect of SiH₃ and the back-interaction with the empty p orbital of boron cause boron to exhibit "metalloid" behavior.
The study found that compounds of the heavier Group 13 elements (Al–In) are extremely air-sensitive and thermally unstable, while NHC-stabilized silylboranes are relatively more stable under inert conditions. Compared to [CH₃]⁻ chemistry, [SiH₃]⁻ chemistry is underdeveloped, primarily due to difficulties in the preparation and handling of silyl salts. This work avoids hazardous routes based on SiH₄ and provides well-defined molecular precursors, potentially aiding in the design of novel main-group chain compounds (B/Al/Ga/In–Si frameworks), thin-film deposition and materials chemistry (volatile hydride precursors), as well as understanding the bonding and reactivity of SiH₃-containing main-group species.
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